The present invention relates to intumescent coatings and, more particularly, to intumescent coatings capable of forming a thick, fine celled, low density foams from a phenol-formaldehyde prepolymer, a blowing agent, and a nucleating agent.
Intumescent coatings are fire retardant coatings which foam (intumesce) and char when exposed to high temperatures and/or flame. Some typical examples of prior coatings are described in U.S. Pat. No. 3,955,987 of 1976 to Schaar and U.S. Pat. No. 4,065,394 of 1977 to Pratt et al. Schaar discloses an intumescent composition comprising monoammonium phosphate, diammonium phosphate, or mixtures thereof; cyanoguanidine, urea or mixtures thereof; sucrose or sucrose and hexanehexol; and titanium dioxide as a heat reflecting agent. Pratt et al discloses an intumescent coating formed from a silicone resin base to which is added an intumescent fire retardant mixture including an oxide of iron and a phosphate of potassium to provide the material with crusting upon exposure to fire; a charring material such as tripentaerythritol and a foaming or blowing agent such as melamine. The Pratt et al coating is adapted for application to metallic surfaces such as aluminum.
Previous intumescent coatings have suffered from one or more disadvantages which have limited their usefulness. For example, in some cases they are excessively heavy and not advantageous for use in air- and spacecraft. Some coatings simply do not provide sufficient thermal protection and others give off noxious smoke and fumes as they char. Still other coatings are difficult to apply to irregular surfaces. In the case of the Schaar coating, this coating is designed to be removed with water and, as such, it is not useful in out-of-doors applications or in applications in which the coating may be exposed to high humidity. Still other coatings spall and ablate away under fire conditions.
Thus, there is a need for intumescent coatings which overcome the limitations of prior coatings. More particularly, there is a need for coatings which can be readily cast from solution which do not smoke or give off toxic fumes upon exposure to intense heat and flames, and which are relatively water-resistant.